A 66-year-old man comes to the office due to several months of progressive lower back pain. The pain is constant and dull and often bothers him during sleep. Initially, acetaminophen provided temporary relief but has not adequately controlled the pain lately. He has had no leg weakness, sensory loss, or bowel dysfunction. The patient is anuric due to end-stage renal disease from hypertensive nephrosclerosis, and he receives intermittent hemodialysis. He does not use tobacco, alcohol, or illicit drugs. Temperature is 37.1 C (98.8 F), blood pressure is 130/86 mm Hg, and pulse is 88/min. Back examination shows midline tenderness over the lumbar area. Lower extremity deep tendon reflexes are normal, and flexor plantar response is present bilaterally. Spine radiography reveals irregular and hyperdense areas of bony sclerosis in the L1 and L2 vertebrae. There are no other bony lesions, fractures, or dislocations. Laboratory results are as follows:
| Complete blood count | |
| Hemoglobin | 10.4 g/dL |
| Leukocytes | 9100/mm3 |
| Serum chemistry | |
| Calcium | 8.4 mg/dL |
| Phosphorus | 5.2 mg/dL |
| Liver function studies | |
| Alkaline phosphatase | 300 U/L |
Which of the following is the most likely cause of this patient's lower back pain?
This elderly man with several months of progressive back pain has focal lumbar tenderness, increased alkaline phosphatase, and L1/L2 sclerotic lesions suggesting osteoblastic bone disease due to metastatic prostate cancer.
Prostate adenocarcinoma is the most common cancer in men and often presents with manifestations of metastatic disease. Symptoms usually arise after spread to the axial skeleton (vertebral bodies, ribs) with resultant progressive lower back pain or acute functional issues (eg, motor weakness, incontinence) from pathologic fracture or spinal cord impingement.
Unlike many other forms of metastatic cancer to the spine, prostate cancer usually causes pure osteoblastic lesions. This leads to normal or low serum calcium (unlike osteolytic disease), elevations in alkaline phosphatase, and imaging evidence of focal, sclerotic bone lesions. Further evaluation with a radionuclide bone scan and prostate-specific antigen test is required. A prostate biopsy is likely needed.
(Choice A) Colorectal cancer often causes abdominal symptoms (eg, pain, change in bowel habits, bleeding) and usually spreads to the liver and lungs. Osteoblastic bone lesions would be atypical.
(Choice C) Multiple myeloma is a plasma cell neoplasm that often presents with bone pain due to lytic lesions (not blastic lesions), hypercalcemia (not normal calcium), anemia, and renal disease.
(Choice D) Paget disease is a common disorder of bone remodeling that is often asymptomatic and diagnosed after incidentally discovering an elevated alkaline phosphatase. Radiographs typically reveal osteolytic lesions or mixed osteolytic/osteoblastic lesions (not osteoblastic alone).
(Choice E) Chronic kidney disease often causes hyperphosphatemia (as in this patient), hypocalcemia, and secondary hyperparathyroidism and is frequently associated with renal osteodystrophy. Manifestations include increased bone turnover, with radiographic evidence of widespread osteopenia and subperiosteal bone reabsorption (not focal, sclerotic lesions).
(Choice F) Vertebral osteomyelitis often causes slowly progressive back pain; however, imaging typically reveals vertebral body destruction and collapse of the disc space (not sclerotic lesions).
Educational objective:
Prostate cancer may initially present with symptoms related to metastatic disease. Spread to the axial skeleton is common, and manifestations typically include slowly progressive lower back pain or functional impairment (eg, motor weakness, incontinence). Prostate cancer usually causes osteoblastic bone lesions with normal or low calcium, elevated alkaline phosphatase, and radiographic evidence of focal, sclerotic lesions.